The late philanthropist and socialite Brooke Astor had a “very nice, cordial relationship” with her son, Anthony Marshall, said Linda Gillies, longtime director of the now-defunct charitable foundation set up by Ms. Astor’s husband, Vincent Astor. “They spoke, they laughed together and they worked together.”

Yet, mother and son inevitably had their moments. Ms. Gillies recalled a particular comment that Ms. Astor made about her son’s new $2 million apartment on East 79th Street. “She said, ‘Tony bought a new apartment,’ rolled her eyes, and said, ‘Guess who paid for that?’”

Ms. Gillies was the first witness called to testify in the case against Ms. Astor’s son, who is charged with stealing from his elderly mother’s reported $200 million fortune. Future witnesses in the high-profile case are expected to include such luminaries as Henry Kissinger, Annette de la Renta and Barbara Walters.

Among the many allegations, Mr. Marshall is also accused of tricking his mother into thinking she was running out of money in order to convince her to sell one of her beloved Childe Hassam paintings for a reported $10 million, with her son earning a cool $2 million commission on the deal.

“She was crazy about that picture,” Ms. Gillies told jurors on Wednesday, April 29. The charity director recalled how Ms. Astor would always comment on the painting whenever the pair walked into her library. “There’s the Childe Hassam,” Ms. Astor would say. “Isn’t it beautiful?”

A day earlier, Mr. Marshall’s attorney, Frederick Hafetz, launched his defense, arguing that the renowned philanthropist had only donated money from her late husband’s charitable foundation, never her own funds, until changing her will in 1993 out of dislike for her son’s wife, Charlene Marshall. (Ms. Astor later revised her will to include Ms. Marshall.)

A key point of debate in the case surrounds Ms. Astor’s mental state as she repeatedly made changes to her will. Ms. Astor, who suffered from Alzheimer’s, died in 2007 at the age of 105.

Taking the stand on Wednesday, Ms. Gillies, dressed in a white jacket and pastel scarf, recalled an incident in 1995 when Ms. Astor had requested a meeting with the Rev. Jesse Jackson. Mr. Jackson would later show up, but, according to Ms. Gillies, “It was clear Ms. Astor couldn’t remember why she had asked him there.”

The charity director nonetheless described her former boss as hugely generous. Prior to dissolving the foundation in 1997, after donating almost $195 million over a span of nearly 50 years, Ms. Astor one day picked up a vase and presented it to Ms. Gillies as a present. “I think it was an expression of affection on her part,” Ms. Gillies said.

The defense immediately seized upon that anecdote as an example of Ms. Astor’s mental capability to give things away as she pleased.